Variable resistance element



Feb. 24, 1959 I J. A. CLEMENT! VARIABLE RESISTANCE ELEMENT Filed Oct. 10, 1955 By Ms 4rr'aQA/Eys .Hee/s, 1675c, 2512? 1,2 2 913 United States Patent VARIABLE RESISTANCE ELEMENT John A. Clementi, Alhambra, Calif., assiguor to Beckmau Instruments, Inc., Fullerton, Calif., a corporation of California Application October 10, 1955, Serial No. 539,501

Claims. (Cl. 201-48) This invention relates to a variable resistance element which is commonly referred to as a potentiometer, and, in particular, to a variable resistance element having means for controlling the contact pressure of the moving contact on the fixed resistance.

In a potentiometer having a contact which traverses a fixed resistance element, the magnitude of the pressure exerted by the moving contact on the fixed resistance affects the useful life of the potentiometer, the torque required to operate the potentiometer, and the electrical noise generated by the motion of the moving contact along the resistance element.

An increase in contact pressure will reduce theelectrical noise, which is often desirable; however, it will also increase the amount of torque required and reduce the useful life of the instrument. The actual contact pressure desired in any particular potentiometer will depend upon the specific application of the potentiometer. Hence, it is seen that where potentiometers are produced in quantity, some method for changing the contact pressure is desirable. It is also found in the manufacture of potentiometers of this type that the distance between the rotating shaft and the fixed resistance element will vary, depending upon the particular resistance element selected and upon the manufacturing tolerances existing. In the manufacture of wire-wound potentiometers, it is convenient to produce units of different resistance values from identical parts by winding the resistance wire on cores of different diameters. This procedure also results in variations in the distance between the rotating shaft and the resistance element. It has been the practice to bend the contact-carrying arm which supports the moving contact to control the magnitude of the contact pressure between the moving contact and the resistance element. This is undesirable because the normal shape of the contact arm is changed and often the bending operation results in damage to some portion of the potentiometer.

It is an object of this invention to produce a variable resistance element of the potentiometer type in which the contact pressure may be varied without bending or otherwise deforming the physical structure of the instrument.

It is another object of the invention to provide a variable resistance element in which the contact carrier is eccentrically mounted on the rotating shaft, and is movable about the rotating shaft guided by the eccentric mount to vary the spacing between the contact end of the carrier and the axis of rotation of the shaft.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes a preferred embodiment of the present invention which is given by way of illustration or example.

In the drawing:

Fig. 1 is a sectional view of a preferred embodiment of the invention;

ice

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1; and

Fig. 3 is an enlarged partial sectional view taken along the line 33 of Fig. l.

A case 10 of the embodiment shown in Fig. l is preferably molded in a unitary piece of nonconducting material, the case comprising a cylindrical shell portion 12 and a back plate 14 of the potentiometer. A front lid 16 having a shoulder 18 which registers with an internal diameter 20 of the case 10 is fixed to the case by a clamp 22. The front lid 16 includes a shoulder 24 and a threaded boss 26 for mounting the potentiometer in an I instrument panel or the like.

A resistance element 27, which may comprise a circular core 28 having a plurality of turns of resistance wire 30 wound thereon, is positioned within the case 10. A shaft 32 is rotatably mounted in the front lid 16 and in a bearing 34 which is mounted in the back plate 14 of the case 10. A block 36 which is preferably made of a nonconducting material is mounted on the shaft 32 by suitable means such as a setscrew 38 inserted in a threaded opening 40 in the block 36. Spacing washers 39 may be placed on the shaft 32 between the front plate 16 and the block 36 to eliminate axial movement of the shaft relative to the case.

The block 36 has a cylindrical surface 42 the axis of which is colinear with the axis of rotation of the shaft 32, and has a second or eccentric cylindrical surface 44 the axis of which is parallel to and spaced from the axis of rotation of the shaft 32. A contact carrier arm 46 is pro vided with a circular opening 48 in one end thereof, the contact carrier being positioned on the block 36 so that the surface 44 is disposed within the opening 48. A spring element 50 having an end bent to form a contact 52 is mounted on the end of the arm 46 opposite the opening 48, the contact portion 52 being urged into engagement with the inside diameter of the resistance element 2.7 by the action of the spring 50. A bushing 54 is mounted on the surface 42 of the block 36 and serves to keep the contact arm 46 in position on the surface 44, the bushing being fixed to the block 36 by suitable means, such as being a press fit thereon. Thus, it is seen that the surface 44 acts as a guide for locating the contact carrier arm 46 between the shaft 32 and the resistance element 27, the contact carrier being movable on the surface to vary its locations therebetween.

Terminals 56, 58 and 60 are mounted in the cylindrical shell portion 12 of the case 10, the terminals providing for electrical-connections to the resistance wire 30 and to the contact 52. A circuit is completed from the terminal 60 to the contact 52 through a brush 62 mounted in the terminal 60 and riding on the bushing 54, the brush, bushing and contact carrier arm being electrical conducting material.

In constructing the potentiometer as described above, the contact pressure may be adjusted in a jig for the rotor before complete assembly, or the unit may be assembled with a front lid having openings therein providing access to the interior of the unit for performing the adjustment operations to be described. In either event, the contact arm 46 is rotated about the shaft 32 on the eccentric surface 44 to produce a desired outward force, at the position of the contact 52 and usually determined by actual meas urement, which will produce the desired pressure of the contact 52 on the resistance winding 30 when the unit is in use. It will be observed that as the contact arm 46 is rotated about the shaft 32, the radial distance of the carrier from the axis of rotation of the shaft changes. thereby providing control over the contact pressure exerted by the spring 50. After the desired amount of pressure is obtained, the contact arm 46 is fixed in place on the block 36 by suitable means, such as soldering to the bushing 54. Thus, it is seen that by the unique construction disclosed herein, the pressure exerted by a moving contact of the potentiometer upon the fixed resistance element may be adjusted without requiring any mechanical deformation of the components of the instrument.

Although an exemplary embodiment of the invention has been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiment disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

I claim as my invention:

1. In a potentiometer having a resistance element arcuatcly disposed in a case, the combination of: a shaft; means for rotatably positioning said shaft within the case, said shaft including an eccentric guide means; a contact arm resiliently carrying a contact directly engaging the inner surface of the resistance element when said shaft is turned, said arm being rotatable about said shaft to vary the pressure exerted by said contact on the resistance element, said arm including means engaging said guide means for moving said arm radially relative to said shaft as said arm is rotated about said shaft; and means for fixing said contact arm to said shaft for movement of said contact along the resistance element concentric with said shaft,

2. ln :1 potentiometer having a resistance element arcuately disposed in a case, the combination of: a shaft means rotatably positioned within the case and having a surface thereon eccentric with the axis of rotation of said shaft means; a contact arm mounted on said surface, said arm resiliently carrying a contact directly engaging different portions of the inner surface of the resistance element when said shaft means rotates within the case, said contact arm being rotatable relative to said shaft means to vary the pressure exerted by said contact on the resistance element; and means for fixing said contact arm to said shaft means at a selected position for movement of said contact along the resistance element concentric with said shaft means.

3. In a potentiometer, the combination of a resistance element arcuately disposed within a case; a shaft rotatably mounted in said case, said shaft having a cylindrical surface the axis of which is parallel to and spaced from the axis of rotation of said shaft; a contact carrier mounted on said surface, said carrier being rotatable on said surface about said axis thereof; a'contact resiliently mounted on said carrier and disposed to directly engage the inner surface of said resistance element; and means for fixing said carrier to said shaft for movement of said contact concentric with said shaft as said shaft is rotated.

4. In a potentiometer, the combination of: a resistance element arcuately disposed within a case; a shaft rotatably mounted in said case, said shaft having a cylindrical surface the axis of which is parallel to and spaced from the axis of rotation of said shaft; a contact carrier having a circular opening therein, said cylindrical surface being positioned within said opening, said carrier being rotatable on sad surface; a contact resiliently mounted on said carrier and disposed to directly engage the inner surface of said resistance element; and means for fixing said carrier to said shaft for movement of said contact concentric with said shaft as said shaft is rotated.

5. In an electrical potentiometer having a resistance element annularly disposed in a case with a shaft rotatably mounted in the case substantially concentric with the resistance element, the combination of: a wiper arm for directly and resiliently contacting the inner surface of the resistance element; means for mounting said wiper arm for eccentric rotation about the shaft to vary the pressure exerted by said wiper arm on the resistance element; and

means for fixing said wiper arm to the shaft in a selected position for rotation by the shaft concentric with the shaft and the resistance element.

- References Cited in the file of this patent UNITED STATES PATENTS 1,247,009 Rhodus Nov. 20, 1917 1,669,687 Adams May 15, 1928 2,429,465 Jenny Oct. 21, 1947 FOREIGN PATENTS 97,698 Germany Oct. 18, 1896 737,848 France Oct. 10, 1932 396,877 Great Britain Aug. 17, 1933 

